Carbon nanotubes (CNTs) are molecules made of pure carbon with a chemical structure similar to rolled sheets of graphite, typically with one end capped. The tubes typically have diameters on the order of a few to a few hundred nanometers, while their length can be up to a few micrometers. Due to the unique structure of CNTs, they have excellent physical, electrical, mechanical and chemical properties that make them suitable for many different applications. For example, CNTs may be the most efficient material for field emission.
Field emission displays (FEDs) are an emerging and rapidly developing flat panel display technology developed as an alternative to bulky cathode ray tube (CRT) displays. FEDs have the advantages of low weight and a thin profile, similar to liquid crystal displays (LCDs), combined with a wide viewing angle, high brightness, and low energy consumption.
Typically, FEDs have a triode structure consisting of an anode, cathode and gate electrode. In conventional FED processing, a fluorescent material is formed on an anode substrate, and an electron-emitting source with a discharge tip is formed on a cathode substrate facing the anode substrate. A gate electrode and an insulating layer are also formed on the cathode substrate, with openings through the gate electrode and insulating layer for the discharge tips. By applying a voltage to the gate electrode, electrons are released from the discharge tips and are accelerated toward the anode substrate to strike the fluorescent material (e.g., red, blue and green phosphors), resulting in light emission from the phosphors. A thousand discharge tips may compose a single pixel on the display. Traditionally, molybdenum has been employed as the electron-emitting source and fabricated into discharge tips, despite various processing and cost issues. Discharge tips formed from CNTs are being investigated as a possible alternative.
Despite their excellent properties and potential applications, CNTs are plagued by processing challenges that may limit commercial usage of these materials. For example, CNTs are difficult to align or disperse due to their strong affinity for each other, which is caused by van der Waal forces. Pure CNTs are long ropelike molecules that may be disordered and intertwined with each other, resembling a plate of nanoscale spaghetti. In an attempt to produce vertically aligned carbon nanotube arrays, CNTs have been grown from metal catalysts or seed particles (e.g., nickel) patterned on a substrate. Such CNTs may be difficult to produce and to activate individually, however, since the CNTs tend to clump together.
To exploit the properties of the CNTs in high definition displays and other electronic devices, it would be advantageous to develop a method to evenly disperse and align the nanotubes.